In the operation of circular knitting machines, the knitting needles are moved upwardly and downwardly in the tracks or grooves of the needle cylinder by cam mechanisms that engage butts on the knitting needle as the cylinder rotates. Certain circular knitting machines include both a needle cylinder and a dial with knitting needles sliding outwardly and inwardly in grooves or tracks in the dial. In such certain circular knitting machines, two sets of cam mechanisms are provided and the timing of the operation of the two sets of knitting needles and cam mechanisms must be properly coordinated.
Most, if not all, circular knitting machines currently being manufactured and sold are multiple-feed knitting machines with, for example, 48 feeds around a 30 inch diameter needle cylinder and dial. It is desirable to provide a needle selection mechanism which permits selection of any one of three needle positions for the knitting needles at each of these multiple feeds.
My U.S. Pat. No. 4,956,981, assigned to the assignee of this application, discloses a needle selection system in a multiple feed circular knitting machine that permits such selection of any one of three dial needle positions at each of the yarn feeds. While providing a needle selection system which accomplished many of the desired functions of such a needle selection system, my prior needle selection system had several disadvantages and deficiencies.
Foremost among these disadvantages and deficiencies is that this prior needle selection system required guide or cam parts that are very small (microcams) that are complicated and expensive to manufacture and are highly susceptible to being broken when removed from the knitting machine. Moreover, such microcam parts do not limit unnecessary and undesirable movements of the knitting needles when in the tucking and welting positions. Also, my prior needle selection system could not accommodate a fourth dial needle position (i.e. a supporting or withdrawn position) without changing the cam positions of the knitting and tucking cams. A still further deficiency of my prior needle selection system, as disclosed in U.S. Pat. No. 4,956,981, is that the knitting needles are advanced to the knitting position by engagement with both a tucking cam and a knitting cam which can lead to instability in the needle operation at high knitting speeds. Finally, there is a danger with my prior needle selection system when the dial knitting needles are in the supporting and welt positions, that these needles may prevent the supply of yarn to the knitting needles that are in the knitting or tucking positions.